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02-11-2009, 05:40 PM   #1
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Auto Revuenon 135mm lens not stopping down

Hi, I would like to ask for some help, I am not really experienced (yet ) with the Pentax (D)SLR system.

My problem is that my Auto Revuenon 135mm f/2.8 PK mount lens does not stop down. The symptoms are the following: in case if I just mount the lens on my K10D, whatever f-number I set on the lens it just stays in f/2.8. However, if I mount a macro extension ring between the lens and body everything works just fine.
The lens had the Ricoh pin removed by the previous owner, at least is was mentioned in the ebay listing.

Below I attach some photos with the lens mount.

I would need quick advice because I am leaving soon for a trip and I would like to know whether to take the lens with myself or just take another one instead.

Thanks in advance for the help.
psz



02-11-2009, 06:26 PM   #2
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One question:
  • Are you shooting in "M" mode?
The lens will not stop down except in "M" (Manual exposure) mode with a non-A K-mount lens.

Steve
02-12-2009, 03:25 AM   #3
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As far as I know and experienced, M and Av modes works fine with non-A lenses, I am using both modes. Anyway, the mode shuold be irrelevant because the DOF preview has to work, doesn't it? But with this lens it doesn't, and as I said if use a simple extension tube the DOF preview starts to work.

The only difference that could be an issue is the width of the aperature lever. This Auto Revuenon has 5mm wide lever while regular Pentax lenses (also the macro tube I was using) have 3mm wide lever. Nevertheless, I have looked carefully at the in the aperature mechanics of camera and I can't see any reason why would not stop down a lens with wider lever.
02-12-2009, 09:04 AM   #4
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- Remove the bayonet mount to access the lever ring and take it out.

I didn't even realize until Steve mentioned that one could stop down even in 'M' mode (can you pslizard?).

Its not a question of the modes working, but of the body blocking the aperture lever and keeping the lens open.

K.

02-12-2009, 09:59 AM   #5
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Thanks for the comment thePiRaTE!!. However, as I don't fully understand what do you mean, I have the feeling that I am lacking some basic knowledge about how stopping down works on the Pentax digital system. Could you please summarize in short the things I need to know and what I need to do with the lens.

I forgot to mention, that with my MZ-5n the lens works fine -- at least it work as I expect: when I stop down it still keeps the lens in f/2.8 so that the viewfinder is the brightest possible but in the meanwhile the metering knows about the fact that the lens is getting stopped down as it adjusts the exposure time with each click. Moreover, the with DOF preview the effect of smaller aperature also gets visible.
Now, with my K10D nothing works, except with f/2.8. The metering does not adjust with stopping down and the DOF preview does not show any sign of the lens being stopped down. As I mentioned only if I mount the lens with a macro tube at least the with the DOF preview the lens is stopped down (although the metering still does not work).

I would be really grateful if someone could point out what am I doing in the wrong way/what is different compared to the MZ-5n and my straight logic :P

Thanks!
02-12-2009, 10:20 AM   #6
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The digital system uses the 'A' setting to electronically trip the aperture lever as I understand it. Without the 'A' contact, there is nothing to tell the camera to move the lever, so it stays put holding the aperture open. Since the lens is designed to let the body control the aperture, you can dial all you want and nothing will happen on the digital body.

So, you need to remove the aperture lever from the lens in order to stop down manually with the digital body in Av mode (not sure about 'M' as mentioned by Steve, did you try it?)

K.
02-12-2009, 11:19 AM   #7
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QuoteOriginally posted by thePiRaTE!! Quote
... (not sure about 'M' as mentioned by Steve, did you try it?)

K.
If the aperture ring is enabled and the camera does not detect the support for body-controlled aperture (No "A" setting or the aperture ring is not in the "A" position) the lens will not stop down unless in M mode. This information is on page 210 in the K10D manual, but not that clearly stated. There are reasons for this behavior that are outside the scope of this thread so I won't go into them.

As to why it works with the extension tube...if the extension tube is "non-Auto" (i.e. without aperture coupling), the lens will have full manual aperture (always stopped down). That would be my best guess anyway.

Steve
02-12-2009, 01:48 PM   #8
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QuoteOriginally posted by stevebrot Quote
...As to why it works with the extension tube...if the extension tube is "non-Auto" (i.e. without aperture coupling), the lens will have full manual aperture (always stopped down). That would be my best guess anyway.

Steve
Ah, that makes sense, and finally ties the whole thread together. I didn't understand anyone's advice until I read that.

The reason the lens works properly on an MZ-5n is that Pentax has left a lever called the aperture simulator off its digital camera K mount (some film cameras too). You can compare your cameras and see the lever, on the right side of the mount. It goes into a slot on the lens mount, at the bottom and out of focus in your picture. There's a lever in there that moves with the aperture ring to tell the camera what the ring is set to.

Without the aperture simulator on the camera, lenses like this have strange properties. Metering can't be done in the normal way because the meter doesn't have aperture information. Modes other than M don't work right without that information either. In M mode, you can get the meter reading by using the DOF preview or green button. That temporarily stops down the lens to the setting on the aperture ring and measures light. Then you can take the photo, and the camera will use the same aperture ring setting.

The Pirate is recommending disabling the aperture lever, which would allow the use of the aperture ring in Av mode. This is probably easy on this lens because it is a third-party manufacturer. The aperture control is a two-part mechanism, with the external lever connected to the mount and moving a secondary lever inside the lens. (That way the manufacturer could easily adapt the lens to different mounts.) Disabling the lever means the camera won't hold the lens wide open for focusing, so the aperture is always at its ring setting. You can use Av mode then. There are drawbacks - a darker viewfinder, and your MZ-5n will be confused.

It is the kind of thing that some photogaphers are OK with and some will hate. For vacation, it might not be a great time to learn.

02-12-2009, 05:26 PM   #9
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First of all, Dave, Pirate, and Steve: thanks for the detailed information, now things are getting clear.

However... considering the option to make the lens more digital-compatible, I've decided to give it a try, I am generally the DIY type. I supposed that "disabling the aperture lever" means somehow removing it and of course hoped that this could be reversible.
However, when I took off the lens mount realized that taking out the inner rotating part which holds the aperture lever is not really possible -- at least not in a reversible way because the aperture lever moves on a ring with ball bearings

Any ideas?

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